This invention relates to a method and apparatus for regenerating used activated carbon, and more particularly to a method and apparatus for controlling the electrical resistance of the layers of used activated carbon to be regenerated when it is heated and regenerated by passing electric current therethrough in an electric furnace.
Due to shortage of industrial water, especially waste water is purified by the adsorption function of activated carbon for the purpose of reusing the purified water. However, as activated carbon is expensive, it is desirable to efficiently regenerate used activated carbon which has adsorbed impurities during the purification of water.
To regenerate used activated carbon it is necessary to heat it at a temperature of from 400.degree. to 800.degree. C. or more and to cause it to contact with steam. According to one prior art method of regeneration, the used activated carbon was contacted with hot combustion gas. However, with this method, a portion of the activated carbon is lost by combustion so that it is necessary to supplement the lost portion with fresh activated carbon and a substantial portion of the running cost of the water purifying apparatus, in an extreme case more than one half of the cost, is occupied by the cost of supplementing the fresh activated carbon. Especially, in the case of a small capacity furnace this tendency is remarkable so that this method is not efficient where such small quantity of used activated carbon is to be regenerated which has been used for the treatment of ordinary waste water.
As a result of our research we have found that the electrical resistance of used activated carbon varies with time in the following manner when it is regenerated by the passage of electric current.